The general development trend of power electronics devices, such as frequency converters, is an increase in power density. It is known in the art that handling of high power in a small-sized device requires effective cooling of the power components, for example with liquid cooling, i.e. by transferring the dissipation power via liquid circulation from the components to outside the device.
High power electronics devices, like liquid cooled frequency converters or their separate submodules, are normally mounted inside enclosures which ensure e.g. the electric safety of the user. In spite of that the structures which are in contact to the components producing major part of the power dissipation are effectively cooled by liquid, power dissipation will normally be generated also in some other parts which are not cooled by liquid, e.g. in fuses, high power busbars, printed circuit boards (PCB), and the like. This power loss, in combination with warm surfaces of the high power liquid-cooled structures, cause warming of the air inside the enclosure to an extent that may be harmful for e.g. to components on PCBs.
The interior air of an enclosure can be cooled by circulating external air through it. This, however, may be problematic e.g. in dirty environments wherein a high degree of protection of the enclosure is required.